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Pronounced Zonal Heterogeneity in Eocene Southern High-Latitude Sea

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Pronounced Zonal Heterogeneity in Eocene Southern High-Latitude Sea Supporting Information Douglas et al. 10.1073/pnas.1321441111 SI Text Spiniferites spp., and even typical low-latitude taxa such as Apec- Further Details of the La Meseta Formation Dinocyst Biostratigraphic todinium spp. (7). Age Model. As is the case for any biostratigraphic age assignment, It is conceivable that the Weddell Sea harbored the trans- one has to assume relative synchronicity between different bio- antarctic fauna earlier than other Southern Ocean locations, and events, in this case between the East Tasman Plateau (65°S pa- excluded cosmopolitan taxa due to cooler temperatures, but there leolatitude), the Wilkes Land Margin (67°S), and Seymour Island is no independent evidence to suggest this at present. Notably, (67°S). Ocean circulation patterns derived from fully coupled there is no statistically significant correlation between the quan- ocean–atmosphere models as well as biogeographical data suggest titative distributions of endemic taxa and SST (8). The last oc- that both the southwest Pacific Tasman Sector and Seymour Is- currences of Arachnodinium antarcticum and Hystrichosphaeridium land were under the influence of Antarctic-derived ocean currents truswelliae are well documented to fall within Chron C18n (1, 2). There are no described geographic discrepancies in bio- (∼38 Ma) (3, 5). Both taxa occur in the sample from TELM 3. The stratigraphic evolution along the Cenozoic Antarctic margin, al- combined occurrence of E. diktyostyla and these taxa place the age though there are relatively few data for Antarctic biostratigraphy of TELMs 2 and 3 to between 45 and 38 Ma (Fig. S1). (3). Importantly, circumantarctic Paleogene dinocyst assemblages Enneadocysta diktyostila and a morphologically closely related constitute dinocysts that are produced by presumed autotrophic species, E. multicornuta, are abundant in samples from TELM 5. dinoflagellates (i.e., the gonyaulacoid cysts) and heterotrophic Alterbidinium distinctum is present in samples from TELM 5 and dinoflagellates (peridinioid cysts; see ref. 4 for further discussion). above. Its first consistent abundance at the East Tasman Plateau This suggests that a relatively wide array of environmental con- is at a level close to the middle-late Eocene boundary (top Chron ditions, perhaps on a seasonal scale, affected dinocyst assemblage C17n, ∼37 Ma), although spot occurrences are also reported in structure. It therefore seems unlikely that any diachronicity in older strata (3). Protoperidinioid dinocysts, mainly the heterotrophic dinocyst events arises from biogeographic isolation or differential taxa of Brigantedinium spp., Lejeunecysta spp., and Selenopemphix environmental conditions between Seymour Island and the ref- nephroides, are also present in samples from TELM 5 and above. erence sections at the East Tasman Plateau (3, 5) and on the The first abundant occurrence of these taxa at the East Tasman Wilkes Land Margin (6, 7). Plateau dates to the late middle Eocene (∼41 Ma) (12, 18), in- The dominant palynomorph groups in the La Meseta samples creasing in abundance in the late Eocene of the East Tasman are dinocysts, Paralecaniella and terrestrial palynomorphs, pri- Plateau (12, 19, 20). TELM 5 and 6 samples are devoid of A. marily Nothofagus. The preservation of the palynomorphs is good to antarcticum and H. truswelliae, potentially suggesting an age excellent, but they are quite rare in the palynological residues, younger than 38 Ma, but these taxa are rare overall and hence which are dominated by minerals insensitive to palynological sam- their absence is not necessarily diagnostic. Collectively, the di- ple processing. nocyst occurrences suggest an age older than 37 Ma for TELM 5, Samples from the Tertiary Eocene La Meseta stratigraphic but younger than 41 Ma. units (TELMs) 2–3 are characterized by abundance of typical Dinocyst assemblages in TELM 7 sediments are atypical, and these Antarctic-endemic taxa (8), notably Enneadocysta diktyostila, samples are dominated by Nothofagus pollen and Paralacaniella Vozzhennikovia apertura, Spinidinium macmurdoense, Deflandrea (Table S1). Strontium-isotope ratios from the upper part of TELM antarctica,andOctodinium askiniae. Samples from TELM 3 also 6 and TELM 7 correlate well with the global seawater 87Sr/86Sr include Arachnodinium antarcticum and Hystrichosphaeridium curve (11), suggesting that the age assignments posited by ref. 9 for truswelliae. Cosmopolitan taxa such as Operculodinium spp. and this part of the record are accurate. This means that the bulk of Spiniferites spp. are present in low abundances. Based on low overall TELM 6 is ∼41 Ma or younger, consistent with dinocyst indicators 87Sr/86Sr ratios derived from bivalve carbonate, the deposition of foranearlieragedown-section. Importantly, there is no indication TELMs 2–3 was tentatively assigned an early Eocene age (55–51 that TELM 7 sediments are as young as early Oligocene. First, there Ma) (9, 10). Variability in 87Sr/86Sr ratios, however, suggested that is no dominance of protoperidinioid taxa, which would indicate high other factors, such as freshwater mixing or incorporation of trace productivity in sea-ice–influenced conditions, commencing in the silicate minerals, could have biased the strontium-isotope data. The earliest Oligocene (6). Second, typical Southern Ocean markers uncertainty is heightened by the small degree of variance in the for the latest Eocene through earliest Oligocene interval, such as global marine strontium-isotope seawater curve for the early to Deflandrea sp. A., Stoveracysta kakanuiensis, Stoveracysta ornata, middle Eocene (11). The new dinocyst data suggest instead that the Turbiosphaera sagena, and Malvinia escutiana are not recorded in the lower part of the La Meseta Formation is no older than the base of sediments from TELM 7 (19, 21, 22). Strontium-isotope ratios for the middle Eocene, for two reasons. (i) The first occurrence of E. uppermost TELM 7 bivalve carbonates are therefore considered diktyostila (earlier assigned to Enneadocysta partridgei)(5,12) areliableindicatorthattheEocene–Oligocene boundary lies at the dominant in these samples, has been calibrated to Chron C20r top of the TELM 7 (23). (∼45 Ma) (3). (ii) E. diktyostila, Vozzhennikovia apertura, and es- sentially all other taxa present in these samples belong to the so- Standardization and Calculation of Δ47-Derived Paleotemperatures. called transantarctic fauna (13). This group of dinocyst taxa is There are no official standards for Δ47. However, several work- often referred to as Antarctic endemic, because it is biogeo- ing standards, including Carrera marble, NBS-19, cylinder CO2, graphically restricted to the circum-Antarctic Southern Ocean in and two speleothem samples, accurately characterized previously the Paleogene (8). Recent studies have shown that the onset of by numerous measurements (24, 25), were used to test for sys- dominance of these endemic dinocyst taxa around the Southern tematic errors over time and to correlate the Yale mass spec- Ocean started close to the early–middle Eocene boundary (∼49 trometer to the measurements performed in Caltech for the Ma) (8). In contrast, dinocyst assemblages spanning the early original Δ47 thermometer calibration (26). In addition, recent Eocene at the East Tasman Plateau (8, 12), the Wilkes Land interlaboratory calibration experiments (25) involving the mea- Margin (14), and New Zealand (15–17) are dominated by cos- surement of CO2 at isotopic equilibrium obtained through mopolitantaxasuchasDeflandrea oebisfeldensis, D. phosphoritica, CO2—H2O isotope exchange at several temperatures, were used Douglas et al. www.pnas.org/cgi/content/short/1321441111 1of13 to characterize mass-spectrometric isotope effects through com- from 11.8 to 12.0 °C, an increase of 0.2 °C. Five-percent resetting parison with gas-phase theoretical values (27). This standardiza- leads to a Δ47 value of 0.694‰ (13.0 °C), and 10% resetting tion is consistent with the Yale carbonate working standards leads to a Δ47 value of 0.689‰ (14.3 °C). The shift in inferred approach and allows direct comparison of our data with published temperature under 10% resetting, 2.5 °C, is equivalent to the Δ values from other laboratories (28). 47 values are presented here typical analytical error of our Δ47 analyses (Table S3). in both the original laboratory and absolute reference frames (25). Under the extreme burial scenario (Δ47 of reset bonds = Δ Temperatures were calculated from standardized 47 values 0.232‰), 1% resetting of carbonate shifts the shell Δ47 to using the calibration of ref. 26, as revised by ref. 28: 0.695‰, equivalent to a shift from 11.8 to 12.8 °C, an increase of 1.0 °C. Five-percent resetting leads to a Δ47 value of 0.677‰ 6 10 (17.0 °C), and 10% resetting leads to a Δ47 value of 0.653‰ Δ47 = 0:0526 × + 0:0520; [S1] T2 (22.6 °C). This scenario is unrealistic, as there is no evidence that these samples were exposed to very high temperatures. Replace- 13 —18 (where T is in Kelvin) and Δ47 values are given in the original ment of either carbon or oxygen atoms in C O by solid-state reference frame used by ref. 26. This calibration was developed diffusion would lead Δ47 in the direction of a random distribution based on synthetic calcite, but has been tested using modern (Δ47 = 0.232‰ for carbonates) but at the low burial temperatures biogenic carbonates grown at known temperatures. reflected by the infilling cement and the relatively short burial External as well as internal precision should be taken into time associated
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